The invention is directed to a multi-coordinate probe according to the preamble of claim 1. A plurality of measuring and switching multi-coordinate probes is known. In all types of probe it is of particular importance that the stylus after being deflected in any direction again returns to its defined zero position. Various attempts were therefore made to design a bearing arrangement of the stylus in the probe housing in a particularly advantageous fashion.
A probe is indicated in DE-OS No. 28 41 424 which comprises a three point bearing arrangement. Three V-grooves are arranged in star fashion in the probe housing base. Three pins with spherical surface are rigidly attached to the probe retainer. The probe retainer is urged by means of a spring in direction of the probe housing base and the pins assume a fixed position in the associated V-grooves, into which they are to return after a deviation of the stylus.
Furthermore from the EP-ANo. 2-0 088 596 a probe with a bearing arrangement is known which also exhibits three bearing points. The bearing or support points are distributed in one plane uniformly concentrically to the stylus axis. Three balls are arranged in the probe housing base, which for purpose of installation are displaceable parallel to the stylus axis. The three counterbearings at the probe retainer are designed differently. One counterbearing is designed as a security against twisting in the shape of a conical bore. The second counterbearing exhibits a V-groove, which is oriented fixedly towards the center point of the probe retainer. A third counterbearing is a flat support, perpendicular to the stylus axis and perpendicular to the force components of the pressure spring.
By means of differing constructions of the individual bearing or support points it was attempted in the state of the art indicated in the EP-ANo. 2-0 088 596 to avoid a static overdefinition but also an underdefinition. Because of the differing construction of the individual bearing points (ball/cone, ball/prism and ball/plane) the elasticity of the individual support points is, however, also different, which has an unfavorable effect upon the accuracy of the switching point.
These types of support arrangements are to be designated as classical support arrangements, which are shaped in accordance with the "Maxwell Conditions" (see M. Pollermann, "Components of Physical Technology", 2nd Edition, Chapter 4 Guides and Support Arrangements-; Springer Publishing House 1972).
On top of that it is known in multicoordinate probes that measuring force differences and the connected therewith switching point differences caused by bending at different probing directions are reduced by increasing the quantity of the bearing or support points. An increase of the quantity of the bearing points raises however the costs for the fabrication of the close tolerance bearing points to a considerable degree, and there exists the danger that the system becomes statically overdefined. As an example for a probe with several bearing points the DE-OS No. 27 42 817 is mentioned.
There, a group of balls is concentrically arranged at the probe retainer in a V-groove. In the housing there is located also a concentric V-groove in which a second group of balls is located. The groups of balls lie opposite each other and each ball of the one group of balls is located between two adjacent balls of the other group of balls.
Each ball has a surface which can come to rest at the two curved surfaces of two adjacent balls. A spring urges the probe retainer toward the housing, and the balls touch each other with their surfaces at points because of the prestress exerted by the spring.
In order to assure that the desired contact occurs between each group of the individual group of balls and two adjacent balls of the other group of balls, the balls are to start off with allowed to freely roll in their grooves, where they then assume positions because of the spring force and the curvature of the surfaces, in which all balls of the one group of balls contact all balls of the other group of balls. The surfaces formed by two adjacent balls of the one group of balls are naturally curved in the same manner with respect to each other as the surfaces of two adjacent balls of the other group of balls and both groups of balls behave in the same manner as far as assuming the mutual positions in the grooves is concerned. In order to attain a complete and rapid orientation of the balls, a comparatively strong spring can be used and the probe can be vibrated, wherein the stylus is axially retained by means of a fixture.
The balls are arranged and oriented in the manner described, while the epoxy resin introduced previously into the grooves is still soft. The resin serving as cement then hardens, while the relative position of the housing and the stylus is maintained without change.
In this type of bearing arrangement of the stylus all contact points have the same elastic properties, but the installation is relatively cumbersome.